Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753417AbZD2GyP (ORCPT ); Wed, 29 Apr 2009 02:54:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751258AbZD2Gx7 (ORCPT ); Wed, 29 Apr 2009 02:53:59 -0400 Received: from cantor2.suse.de ([195.135.220.15]:36867 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751160AbZD2Gx6 (ORCPT ); Wed, 29 Apr 2009 02:53:58 -0400 From: Nikanth Karthikesan Organization: Novell To: Jens Axboe Subject: [PATCH][RFC] Handle improbable possibility of io_context->refcount overflow Date: Wed, 29 Apr 2009 12:21:39 +0530 User-Agent: KMail/1.11.1 (Linux/2.6.27.21-0.1-default; KDE/4.2.1; x86_64; ; ) Cc: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200904291221.40361.knikanth@novell.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3179 Lines: 92 Hi Jens Currently io_context has an atomic_t(int) as refcount. In case of cfq, for each device a task does I/O, a reference to the io_context would be taken. And when there are multiple process sharing io_contexts(CLONE_IO) would also have a reference to the same io_context. Theoretically the possible maximum number of processes sharing the same io_context + the number of disks/cfq_data referring to the same io_context can overflow the 32-bit counter on a very high-end machine. Even though it is an improbable case, let us make it difficult by changing the refcount to atomic64_t(long). Signed-off-by: Nikanth Karthikesan --- diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 012f065..4f5ff79 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -35,9 +35,9 @@ int put_io_context(struct io_context *ioc) if (ioc == NULL) return 1; - BUG_ON(atomic_read(&ioc->refcount) == 0); + BUG_ON(atomic64_read(&ioc->refcount) == 0); - if (atomic_dec_and_test(&ioc->refcount)) { + if (atomic64_dec_and_test(&ioc->refcount)) { rcu_read_lock(); if (ioc->aic && ioc->aic->dtor) ioc->aic->dtor(ioc->aic); @@ -151,7 +151,7 @@ struct io_context *get_io_context(gfp_t gfp_flags, int node) ret = current_io_context(gfp_flags, node); if (unlikely(!ret)) break; - } while (!atomic_inc_not_zero(&ret->refcount)); + } while (!atomic64_inc_not_zero(&ret->refcount)); return ret; } @@ -163,8 +163,8 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc) struct io_context *dst = *pdst; if (src) { - BUG_ON(atomic_read(&src->refcount) == 0); - atomic_inc(&src->refcount); + BUG_ON(atomic64_read(&src->refcount) == 0); + atomic64_inc(&src->refcount); put_io_context(dst); *pdst = src; } diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index a55a9bd..f829bd2 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1282,7 +1282,7 @@ static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq) if (!cfqd->active_cic) { struct cfq_io_context *cic = RQ_CIC(rq); - atomic_inc(&cic->ioc->refcount); + atomic64_inc(&cic->ioc->refcount); cfqd->active_cic = cic; } } diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h index 08b987b..f1a57f4 100644 --- a/include/linux/iocontext.h +++ b/include/linux/iocontext.h @@ -64,7 +64,7 @@ struct cfq_io_context { * and kmalloc'ed. These could be shared between processes. */ struct io_context { - atomic_t refcount; + atomic64_t refcount; atomic_t nr_tasks; /* all the fields below are protected by this lock */ @@ -91,7 +91,7 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc) * if ref count is zero, don't allow sharing (ioc is going away, it's * a race). */ - if (ioc && atomic_inc_not_zero(&ioc->refcount)) { + if (ioc && atomic64_inc_not_zero(&ioc->refcount)) { atomic_inc(&ioc->nr_tasks); return ioc; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/